The present invention concerns structures forming part of an aircraft. More particularly, but not exclusively, this invention concerns an aircraft structure comprising a skin panel, having an outer surface forming an external face of the structure, and an inner surface internal to the structure, and a plurality of stringers extending along a length of the inner surface of the skin panel. The invention also concerns a method of manufacturing an aircraft structure, comprising the steps of providing an external skin panel and providing a plurality of stringers extending along a length of an inner surface of the skin panel.
Traditional wing boxes comprise an upper skin and a lower skin, one or more spars extending along a length of the wing box, a plurality of stringers extending along a length of the skins and a plurality of ribs in between the two skin panels, extending across the width and depth of the wing box. However, the cost of the stringers of the wing box is very expensive and they are vulnerable to damage during manufacture, assembly and maintenance. This is especially so if the stringers are made from composite materials. This is because composite stringers are formed with free edges having exposed laminate layers which, when knocked, can cause flaking (known as delamination) of the laminate layers. In addition, the inner mould lines (IML) of the inner surface of the skin panels and the stringers are complex which requires complicated tooling and manufacture. In addition, a large number of ribs have to be used in order to prevent the structure from buckling. This adds significant weight to the structure, which is undesirable.
US 2010/0006700 discloses an aircraft wing with wing skins made from webbed panels. These panels are made from two face sheets with a stiffening web sandwiched between them. The web has a repeating pattern of a sinusoid across the width of the wing. However, the repeating pattern of the web makes the panels complicated and relatively costly to manufacture. In addition, it is not possible to vary the geometry of the stiffening web. Therefore, the web cannot be optimised based on a predicted load distribution in the wing. Furthermore, the sinusoidal pattern of the web is not particularly efficient.
The present invention seeks to mitigate the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved aircraft structure or method of manufacture of an aircraft structure.